A Tripartite Synapse Model in Drosophila

Tripartite (three-part) synapses are defined by physical and functional interactions of glia with pre- and post-synaptic elements. Although tripartite synapses are thought to be of widespread importance in neurological health and disease, we are only beginning to develop an understanding of glial contributions to synaptic function. In contrast to studies of neuronal mechanisms, a significant limitation has been the lack of an invertebrate genetic model system in which conserved mechanisms of tripartite synapse function may be examined through large-scale application of forward genetics and genome-wide genetic tools. Here we report a Drosophila tripartite synapse model which exhibits morphological and functional properties similar to those of mammalian synapses, including glial regulation of extracellular glutamate, synaptically-induced glial calcium transients and glial coupling of synapses with tracheal structures mediating gas exchange. In combination with classical and cell-type specific genetic approaches in Drosophila, this model is expected to provide new insights into the molecular and cellular mechanisms of tripartite synapse function

Proceedings of the Thirteenth International Society of Sports Nutrition (ISSN) Conference and Expo

Meeting Abstracts: Proceedings of the Thirteenth International Society of Sports Nutrition (ISSN) Conference and Expo Clearwater Beach, FL, USA. 9-11 June 201

Fatty Acids Directly Activate K\u3csup\u3e+\u3c/sup\u3e Channels in Isolated Gastric and Vascular Smooth Muscle Cells: A Dissertation

The purpose of this work was to determine whether arachidonic acid and other fatty acids might directly regulate the behavior of ion channels. Arachidonic acid is known to be liberated from plasma membrane phospholipid upon activation of cell surface receptors, and to subsequently act as a precursor to biologically active metabolites. This study was based on the rationale that the liberated arachidonic acid itself was a potential regulator of plasma membrane ion channels. The effects of arachidonic acid and other fatty acids on the behavior of ion channels were examined in two preparations of isolated smooth muscle cells. In both cell types, K+-selective ion channels were activated both by arachidonic acid and by fatty acids that are not converted to metabolites through the cyclooxygenase and lipoxygenase metabolic pathways for arachidonic acid. These results indicate that metabolites of these pathways did not mediate the fatty acid response. Further, fatty acids were effective in cell-free patches of membrane in the absence of nucleotides and Ca++, showing that signal transduction mechanisms requiring these and other cytosolic factors were not required. Such signaling mechanisms include those involving phosphorylation, cyclic nucleotides, GTP-dependent proteins, and the NADPH-dependent cytochrome P450 metabolic pathway. Thus fatty acids themselves appear to directly activate K+ channels, much as they directly activate several enzymes, and may constitute a new class of messenger molecules acting on ion channels. The two preparations of cells used were gastric smooth muscle cells from the toad, Bufo Marinus, and pulmonary artery smooth muscle cells from the New Zealand White Rabbit. In gastric smooth muscle cells, a previously undescribed K+ channel was activated by a variety of fatty acids. This channel exhibited a conductance of approximately 50 pS, weak voltage-dependence, and K+ selectivity. The fatty acid structural features required for activation of this channel were examined by testing numerous fatty acids. Further, the same K+ channel was found to be endogenously active in the presence of Ca++ at the extracellular surface of the membrane. In pulmonary artery smooth muscle cells, fatty acids activated K+ channels of a recognizable large-conductance type that is activated by Ca++ at the intracellular membrane surface. This channel type has been widely studied but has not been reported in this preparation. Characteristic of the large-conductance, calcium-activated K+ (CAK) channel type, the channels activated by fatty acids exhibited a conductance of approximately 260 pS, strong voltage-dependence, K+ selectivity, and activation by low concentrations of Ca++ (10-7-10-6 M) at the cytosolic surface of the membrane. Lastly, these CAK channels were found to be activated by membrane stretch

Endogenous adenosine inhibits catecholamine contractile responses in normoxic hearts

The importance of endogenous myocardial adenosine in attenuating catecholamine-elicited contractile responses was investigated in perfused oxygenated rat hearts. Perfusion of the isolated hearts with adenosine deaminase potentiated the isoproterenol-induced increases of three contractile variables (left ventricular pressure development and rates of both left ventricular pressure development and relaxation). The peak (maximal, within 30 s) and maintained (after 1 min) increases of the contractile variables caused by 10(-8) M isoproterenol were enhanced by 15-22 and 31-43%, respectively. Adenosine deaminase appeared in epicardial surface transudates of similarly perfused hearts, indicating that the enzyme had entered the myocardial interstitial space. Isoproterenol alone elevated the release of adenosine into coronary effluents of isoproterenol-stimulated hearts, and adenosine deaminase prevented the release of the nucleoside. The higher the level of adenosine in the effluent, the greater the reduction of the peak contractile variables. Phenylisopropyladenosine at 10(-8) M prevented the adenosine deaminase potentiation of 10(-9) M isoproterenol-induced contractile responses. The adenosine analogue at 10(-6) M blocked completely the isoproterenol-produced increases in the contractile variables. These results suggest that endogenous adenosine prevents full mechanical responsiveness to beta-adrenoceptor stimulation in the oxygenated myocardium. In addition, the findings support the notion that adenosine serves as an important negative feedback modulator in the oxygenated heart

Arachidonic acid and other fatty acids directly activate potassium channels in smooth muscle cells

Arachidonic acid, as well as fatty acids that are not substrates for cyclooxygenase and lipoxygenase enzymes, activated a specific type of potassium channel in freshly dissociated smooth muscle cells. Activation occurred in excised membrane patches in the absence of calcium and all nucleotides. Therefore signal transduction pathways that require such soluble factors, including the NADPH-dependent cytochrome P450 pathway, do not mediate the response. Thus, fatty acids directly activate potassium channels and so may constitute a class of signal molecules that regulate ion channels

Direct regulation of ion channels by fatty acids

A variety of fatty acids regulate the activity of specific ion channels by mechanisms not involving the enzymatic pathways that convert arachidonic acid to oxygenated metabolites. Furthermore, these actions of fatty acids occur in patches of membrane excised from the cell and are not mediated by cellular signal transduction pathways that require soluble factors such as nucleotides and calcium. Thus, fatty acids themselves appear to regulate the action of channels directly, much as they regulate the action of several purified enzymes, and might constitute a new class of first or second messengers acting on ion channels

A Distinct Perisynaptic Glial Cell Type Forms Tripartite Neuromuscular Synapses in the <i>Drosophila</i> Adult

<div><p>Previous studies of <i>Drosophila</i> flight muscle neuromuscular synapses have revealed their tripartite architecture and established an attractive experimental model for genetic analysis of glial function in synaptic transmission. Here we extend these findings by defining a new <i>Drosophila</i> glial cell type, designated peripheral perisynaptic glia (PPG), which resides in the periphery and interacts specifically with fine motor axon branches forming neuromuscular synapses. Identification and specific labeling of PPG was achieved through cell type-specific RNAi-mediated knockdown (KD) of a glial marker, Glutamine Synthetase 2 (GS2). In addition, comparison among different <i>Drosophila</i> neuromuscular synapse models from adult and larval developmental stages indicated the presence of tripartite synapses on several different muscle types in the adult. In contrast, PPG appear to be absent from larval body wall neuromuscular synapses, which do not exhibit a tripartite architecture but rather are imbedded in the muscle plasma membrane. Evolutionary conservation of tripartite synapse architecture and peripheral perisynaptic glia in vertebrates and <i>Drosophila</i> suggests ancient and conserved roles for glia-synapse interactions in synaptic transmission.</p></div